The investigators of this Shared Instrumentation Grant proposal request a high performance, multi-detector planar/SPECT imaging system for use as a dedicated research camera to be located in the School of Hygiene and Public Health. The user group this system will support holds NIH funding from six Institutes, including NCI, NIAID, NIEHS, NIDA, NIMH, and NHLBI. The user group currently conducts planar and SPECT imaging studies using gamma-emitting radiotracers labeled with technetium-99m (Tc-99m), iodine-123 (I-123), and indium-111 (In-111) in a variety of animals (mice, rats, rabbits, dogs, sheep and baboons). The studies are conducted during the development of novel radiopharmaceuticals, and for testing of biologically driven hypotheses relevant to physiology, toxicology, drug abuse and mental health. The user group also performs animal and population-based human studies of environmental exposures to toxic agents. In order to carry out these studies effectively, we must be able to obtain high resolution/high sensitivity images under a variety of acquisition conditions on a routine basis. Further, we must be able to process and analyze the acquired data by modern methods. We are requesting the instrumentation, a state-of-the-art, triple-headed Siemens MULTISPECT3, in order to support, expand and extend our current work, and to remain scientifically competitive. Of importance, the camera would be the heart of an imaging facility that provides a framework for research involving not only the present user group, but also members of the local scientific community at large.